[PATCH RFC v5 4/6] iommu/arm-smmu-v3: Support shared SIDs in insert/remove_master
From: Peng Fan (OSS)
Date: Tue Oct 06 2026 - 08:15:23 EST
From: Peng Fan <peng.fan@xxxxxxx>
On SoCs like NXP i.MX95 where the SMMU has a limited number of Stream
IDs (e.g. 6-bit bus = 64 SIDs), multiple DMA-capable devices are
assigned the same Stream ID by hardware design.
Refactor arm_smmu_find_master() into arm_smmu_find_stream() to look up
streams by SID inside the lock. When a second master attempts to use a
SID that is already claimed, link the masters together via the stream's
shared_masters list instead of rejecting the probe.
Sharing is restricted to single-SID masters (num_streams == 1) to keep
the STE lifecycle simple. Multi-SID sharing is explicitly rejected.
On removal, a shared master detaches from the shared_masters list. The
stream and its RB tree entry are kept alive until the last master using
that SID is removed.
Suggested-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-iommu/arG6hmng3NddGEHm@xxxxxxxxxx/
Assisted-by: LLM
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 92 ++++++++++++++++++++---------
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 3 +
2 files changed, 66 insertions(+), 29 deletions(-)
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 69c2c3596b06a..d306e4af90ef0 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2044,8 +2044,8 @@ static int arm_smmu_streams_cmp_node(struct rb_node *lhs,
&rb_entry(lhs, struct arm_smmu_stream, node)->id, rhs);
}
-static struct arm_smmu_master *
-arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
+static struct arm_smmu_stream *
+arm_smmu_find_stream(struct arm_smmu_device *smmu, u32 sid)
{
struct rb_node *node;
@@ -2054,7 +2054,20 @@ arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
node = rb_find(&sid, &smmu->streams, arm_smmu_streams_cmp_key);
if (!node)
return NULL;
- return rb_entry(node, struct arm_smmu_stream, node)->master;
+ return rb_entry(node, struct arm_smmu_stream, node);
+}
+
+static struct arm_smmu_master *
+arm_smmu_find_master(struct arm_smmu_device *smmu, u32 sid)
+{
+ struct arm_smmu_stream *stream;
+
+ stream = arm_smmu_find_stream(smmu, sid);
+ if (!stream)
+ return NULL;
+ if (!list_empty(&stream->shared_masters))
+ return NULL;
+ return stream->master;
}
/* IRQ and event handlers */
@@ -4109,36 +4122,41 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
kfree(master->streams);
return -ENOMEM;
}
+ INIT_LIST_HEAD(&master->shared_masters_elm);
mutex_lock(&smmu->streams_mutex);
for (i = 0; i < fwspec->num_ids; i++) {
struct arm_smmu_stream *stream;
- struct rb_node *existing;
u32 sid = fwspec->ids[i];
ret = arm_smmu_init_sid_strtab(smmu, sid);
if (ret)
break;
- existing = rb_find(&sid, &smmu->streams,
- arm_smmu_streams_cmp_key);
- if (existing) {
- struct arm_smmu_master *existing_master =
- rb_entry(existing, struct arm_smmu_stream, node)
- ->master;
-
+ stream = arm_smmu_find_stream(smmu, sid);
+ if (stream) {
/* Bridged PCI devices may end up with duplicated IDs */
- if (existing_master == master) {
- master->streams[i] = rb_entry(existing,
- struct arm_smmu_stream, node);
+ if (stream->master == master) {
+ master->streams[i] = stream;
continue;
}
- dev_warn(master->dev,
- "Aliasing StreamID 0x%x (from %s) unsupported, expect DMA to be broken\n",
- sid, dev_name(existing_master->dev));
- ret = -ENODEV;
- break;
+ if (master->num_streams != 1 ||
+ stream->master->num_streams != 1) {
+ dev_warn(master->dev,
+ "Shared StreamID 0x%x not supported for multi-SID masters\n",
+ sid);
+ ret = -ENODEV;
+ break;
+ }
+
+ if (list_empty(&stream->shared_masters))
+ list_add_tail(&stream->master->shared_masters_elm,
+ &stream->shared_masters);
+ list_add_tail(&master->shared_masters_elm,
+ &stream->shared_masters);
+ master->streams[i] = stream;
+ continue;
}
stream = kzalloc_obj(*stream, GFP_KERNEL);
@@ -4148,6 +4166,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
}
stream->id = sid;
stream->master = master;
+ INIT_LIST_HEAD(&stream->shared_masters);
rb_find_add(&stream->node, &smmu->streams,
arm_smmu_streams_cmp_node);
@@ -4155,6 +4174,7 @@ static int arm_smmu_insert_master(struct arm_smmu_device *smmu,
}
if (ret) {
+ list_del_init(&master->shared_masters_elm);
for (i--; i >= 0; i--) {
int j;
@@ -4193,17 +4213,31 @@ static void arm_smmu_remove_master(struct arm_smmu_master *master)
return;
mutex_lock(&smmu->streams_mutex);
- for (i = 0; i < master->num_streams; i++) {
- int j;
+ if (!list_empty(&master->shared_masters_elm)) {
+ struct arm_smmu_stream *stream = master->streams[0];
- /* Skip duplicated SID pointers already freed */
- for (j = 0; j < i; j++)
- if (master->streams[j] == master->streams[i])
- break;
- if (j < i)
- continue;
- rb_erase(&master->streams[i]->node, &smmu->streams);
- kfree(master->streams[i]);
+ list_del_init(&master->shared_masters_elm);
+ if (list_is_singular(&stream->shared_masters)) {
+ struct arm_smmu_master *last;
+
+ last = list_first_entry(&stream->shared_masters,
+ struct arm_smmu_master,
+ shared_masters_elm);
+ list_del_init(&last->shared_masters_elm);
+ }
+ } else {
+ for (i = 0; i < master->num_streams; i++) {
+ int j;
+
+ /* Skip duplicated SID pointers already freed */
+ for (j = 0; j < i; j++)
+ if (master->streams[j] == master->streams[i])
+ break;
+ if (j < i)
+ continue;
+ rb_erase(&master->streams[i]->node, &smmu->streams);
+ kfree(master->streams[i]);
+ }
}
mutex_unlock(&smmu->streams_mutex);
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index ba430078cbce9..2ed7a66c8b0b8 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -969,6 +969,8 @@ struct arm_smmu_stream {
u32 id;
struct arm_smmu_master *master;
struct rb_node node;
+ bool ste_installed;
+ struct list_head shared_masters;
};
struct arm_smmu_vmaster {
@@ -1017,6 +1019,7 @@ struct arm_smmu_master {
bool ste_ats_enabled : 1;
bool stall_enabled;
bool ats_always_on;
+ struct list_head shared_masters_elm;
unsigned int ssid_bits;
unsigned int iopf_refcount;
};
--
2.34.1